Art of cracking hydrocarbon oils



May 27, 1930. E. c. HERTHEL El A 1,760,357

ART OF CRACKING HYDROCARBON OILS v Filed Jan. -5, 1928 4/ Pressureflistz'lmte INVENTORS i'ugezleCf/erzfbel 7g/ amas dC. fifft 155 1, QM' VATTORNEYS Patented May 27, 1930 -NIT ED STATES PATENT OFFICE EUGENE c.nnnrn'nr. AND mourns DE conon 'rrrrr, or cmcaeo, ILLINOIS, ASSIGN- ons'ro SINCLAIR nnrmme oomrm, or NEW YORK, 1v. xi, A conronn'rrou or AB! 01CRACKING HYDBOOARBON" OILS Application filed January 5, 1928. Serial no.M4583.

I have been subjected to results;

special absorbent condensable constituents are subsequently tinuation ofan application filed June 22,

1926, Serial No. 117,697 which has eventuated into Patent 1,677,773.

In addition to desired lower boiling oils, the products of crackingoperations as usually carried out include gases incondensable exceptunder high pressures and at low temperatures. These incondensable gasestend to carry with them uncondensed but condensable lower boilingconstituents suitable as components of the desired lower boiling oilproduct- The recovery of such uncondensed but condensable constituentsis of course desirable to improve the, yield secured from the crackingoperation, and a number of schemes have been used for this purpose.

For example, such gas mixtures have been subjected to scrubbinoperations with media rom which absorbed separated and recovered bydistillation from the absorbent. Likewise, such gas mixtures scrubbingtreatment with raw oil to be sup lied to the cracking operation so thatabsor able constituents are returned to the cracking operation in theraw oil again to escape with from the cracking operation. Where suchcondensableconstituents are reintroduced directly into the crackingoperation proper, overcracking of such constituents frequently Thisoverc-racking can be avoided, for example, by introducing the raw oil,containing such absorbed condensable constituents into .a refluxingoperation to which the vapors and gases from the cracking operation aresubjected so that absorbed condensable constituents are separated beforethe raw oil reaches the crackingiopera-tion proper, but thisinvolvesloss of heat which otherwise proper. I

k In continuous cracking operations, residual oil is usually withdrawnundistilled from the cracking operation proper. Such residtion,

the gases and vapors in the cracking operation ual oils are withadvantage expanded at lower pressure for separation of oil constituentsas vapors therefrom and these vapors in turn subjected to a refluxingoperation able to be returned to the cracking operation",

Part of the heat of such residual discharged from the craclu'ng 'opera-1 for condensation of heavier components suitproper. oils, as tion, hasbeen returned to the cracking operation proper by various expedients,but complete recovery of this heat is at least unusual in practicaloperation.

According to the present invention, uncondensed vapors and gasesincluding condensable constituents, for example, gasoline components,are subjected to scrubbing treatment with raw oil to be supplied to thecracking operation and, before t e. raw oil with constituents absorbedin the scrubbing operation reaches the cracking operation proper,

the heat of residual oil discharged from the cracking operation isutilized to distill such absorbed condens'able constituents from the rawoil. Any possibility of overcracking such low boiling condensableconstituents is thus avoided at the same time that an important heateconomy is eflt'ected. This invenmoreover, provides a particularlyadvantageous way of effecting the heat transfer from residual oil to rawoil containing 4 absorbed constituents.

According to the present invention, the residual oil discharged fromcracking operation is expanded at a lower pressure for the separation ofoil constituents as vapors therefrom, leaving a pitchy or coky residue,and the resulting vapors are subjected to a refluxing operation intowhich raw oil containing absorbed condensable constituents from thescrubbing treatment is directly introduced, lower boiling components ofthese vapors being taken off and condensed together with the condensableconstituents vaporized from the raw oil while the absorption of heat insuch vaporlzation asslsts' 1n condensing the higher boiling componentsof the vapors being subjected to the refluxing operation, theunvaporized portion, of the raw oil at the same time being preheatedanprlbthereby assisting in condensing the higher iling components of thevapors and forming with the reflux condensate a hot oil mixture suitableto be supplied to the cracking operation proper.

"Objectionable constituents of the residual oil discharged from thecracking operation are not included in this oil mixture as they areseparated in the-initial expansion of the residual oil.

The invention will be further described in connection with theaccompanying drawings which illustrate, in a diagrammatic andconventional manner, an apparatus adapted for carrying out the processof the invention.

The pressure still illustrated is of the general type described inLetters Patent No. 1,285,200 issued November 19, 1918, to the SinclairRefining Company on an application o'f'Edward W. Isom. This particulartype of pressure still is used simply for the purposes of illustration.

This pressure still comprises a bulk supply drum 1, a battery ofvertical heating tubes 2, arranged in a heating furnace, and circulatingconnections 3, 4, and 5 including a circulating pump which is arrangedto force oil from the bulk supply drum upwardly through the heatingtubes and back to the bulk supply drum. Vapors from the bulk supplydruin escape through connection 7 to pass upwardly through reflux tower8, uncondensed vapors escaping from the upper end of the reflux towerthrough connection 9 to condenser 12. This condenser discharges intoreceiver 13 from which the condensate is discharged through connection14, uncondensed vapors and gases escaping through connection 15. Raw oilmay be introduced into the upper end of reflux tower 8 throughconnection 16. Some other refluxing medium, for example, a light oilvaporizing substantially completely under the pressure and at thetemperature prevailing in the reflux tower, may be introduced throughconnection 17. The refluxing operation in reflux tower 8 may beefi'ectedor controlled by either or both of these means. Reflux, and any admixedunvaporized oil introduced into the reflux tower, is returned fromreflux tower 8 to the circulatin'g connection 3 through connection 18.Residual oil is discharged from' the bulk supply drum through connection19 arranged to discharge into expander 20. Connection 21 is alsoprovided for the introduction of oilinto the pressure still. Cool oilfor cooling and lubricating the bearings of the circulating pumpissupplied through connection 22.

Connection 23 is provided for initially charg ing the still at thebeginning of a run and for pumping out the still at the end of a run.

Uncondensed vapors and gases escaping through connection 15 aredischarged into the lower end of scrubbing tower 24 through connections25'and' 26. Other hydrocarbon gas mixtures including, forexample,'gasoplied to the cracking operation is introduced into theupper end of scrubbing tower 24 through connections 31 and 32 by meansof pump 33. After passing through the scrubbing tower the raw oil,containing constitucuts-absorbed in the scrubbing tower, flows throughconnection 34 to tank 35, this tank being provided to give flexibilityto the operation. Additional raw oil may also be supplied to tank 35through connection 36.

A pressure reducing valve 37 is provided in. connection 19,advantageously at a point adjacent the pressure still, to control andrelease the pressure between the still and the expander 20. To promotethe consequent vaporization in the expander, steam, or other hot gaseousmedium may be introduced into the expander. Several baflies'are arrangedin the upper end of expander 20 to inhibit entrainment. Vapors escapethrough this expander through connection 38 into the lower end of tower39 and unvaporized material is discharged through connection 40. Thevapors from the expander pass upwardly through tower 39 and aresubjected to reflux condensation therein, low boiling vapors escapingfrom the upper end of this tower through connection 41 to condenser 42.This condenser discharges into receiver 43 provided with a condensateoutlet 44 andgan outlet 45 for any uncondensed vapors and gases.

Raw oil'containing condensable constituents absorbed in the scrubbingtreatment is introduced into the upper end of tower 39 from tank 35through connections 46 and 47 by means of pump 48. Some supplementalrefluxing medium, for example, a light oil vaporizing substantiallycompletely at the temperature and under the pressure prevailing in thetower, may also be introduced through connection 49. The absorbedcondensable constituents are vaporized from the raw oil by the heat ofthevapors esca ing from expander 20, this vaporization o absorbedcondensable constituents assisting in cooling and condensing the vaporsfrom the expander 20, the latter vapors at the same time being furthercooled and condensed by heat absorbed in preheating the 'unvaporized rawoil. Any low boiling components of these vapors and the absorbed.condensable constitutents vaporized from the raw oil escape throughcondenser 42 in which they are condensed, the

condensate being collected in receiver 43.

Any uncondensed vapors and gases remaining may also be subjected'to thescrubbing I the hot oil mixture not introduce treatment, passing to thelower end of scrubbing tower 24 through connections 45, 25 and 26. Theoil mixture collecting in the lower end of tower 39 is introduced intothe pres sure still by means of pump 50, either through connections 51and 16 or through connection 21, or partly through each. of theseconnections. It is advantageous to introduce as much as possible of thisoil mixture through connection 16, but if the oil mixture is too hotmore than a certain amount cannot be introduced into the upper end ofreflux tower 8 while maintaining an appropriate temperature at the topof this tower, unless the vapors in the reflux tower are subjected tosup lemental cooling. Such supplemental coo mg may be supplied byintroducing additlonal raw oil through connections 31, 52 and 16 or byintroducing a supplemental refluxing medium through connection 17. An,part of through connection 16 may be introduced into the pressurestill'through connection 21.

Usually, asingle scrubbing tower 24;, expander 20, expander reflux tower39, and associated condenser and receiver 42 and 4.3 may with advantagebe combined with a number of cracking units. Connections 53, 54, 55, 56and 57 are provided for connecting the recovery system, including theexpander and expander tower, to a batter of pressure stills, each withan associated re paratus as wellas hot connections are advantageouslylagged or heat insulated to prevent heat loss.

In operation, the pressure still is charged with suflicient oil andbrought to cracking condition of temperature and pressure. In a still ofthe type illustrated, an initial charge of about 8,000 gallons of cooloil, say at a temperature of about 80 F., is commonly use The pressuremaintained during the operation is determined to a largemeasure by thestocks to be treated and the products P to be obtained. With gas oilcharacter charg- 1 ing stocks pressures up to 125 pounds .per squareinch or more may be used and with charging stocks containing largeamounts of kerosene character components much higher pressures, say upto 300'pounds per square inch or more, may be used in the production ofgasoline. The pressure in the still system may be maintained andregulated by means of valve 58 in the vapor line between the re fluxtower and the condenser, or by valves I objectionable value thedischarge of residual arranged beyond the condenser or receiver.Duringthe initial period of'operation, residual oil is not dischargedfrom the pressure still, or is discharge-d in but small amount,

but before the pitch concentration in the charge of oil in the pressurestill reaches an oil is begun and the rate of discharge is regulated,with respect to the rate at which raw ux tower. It Wlllbe understoodthat the hot parts of the ap,

of pitch in .the pressure still charge below an objectionable value. Theresidual oil is discharged into expander 20 where a pressuresubstantiallylower than that prevailing within the pressure still ismaintained, the pressure between the still and the expander beingreduced by means of valve 37. Due to this reduction in pressure, thedischarged residual oil is subjectedto further vaporization, vaporsentering reflux tower 39 and pitchy or coky components separating in aresidue remaining unvaporized. The degree of vaporization in theexpander can be controlled by regulating the pressure therein. 'As muchas or more of the residual oil may be so vaporized, but if a liquidresidue isto be obtained it is usually not desirable to go much beyondthis point and it ma be necessary to reduce the amount of vaporlzation,although a liquid residue can sometimes be obtained with vaporization ofas much as 90% or more of the residual oil. Withstill pressures in theneighborhood of100 pounds per square inch or higher, the pressure in theexpander may be maintained at a value between atmospheric pressure andsay 50 pounds per square inch or higher, depending upon the amount ofvaporization desired. In the production of gasoline from a gas oilcharacter stock, for example, thetemperature at the top of reflux tower8 may be maintained at about 550 F. and -the temperature at the top ofexpander reflux tower 39 at about 350 F. The temperature at the top ofreflux tower 8 is maintained by regulated introduction. of raw'oil orthe oilmixture from tower 39 through connection 16 or of a mixture of'cool raw oil and the hot oil mixture from tower 39 through thisconnection, or b the introduction of some other refluxing me ium, suchas a part of the distillate product, through connection 17, or by thesemeans con-- jointly. The temperature at the top of exander reflux tower39 is maintained by the regulated introduction of raw oil throughconnection 47, supplemented as may be necessary by the regulatedintroduction of some other refluxing medium, such as a part of thedistillate product, through connection 49. The temperature of the oilmixture collecting in the bottom of expander reflux tower 39 mayapproximate 450-480 F., and it is usually desirable to limit thetemperature of the oil or oil mixture introduced'into reflux tower 8 toa value not exceeding 2759 to 280 .F. to maintain a head temperatureapproxie mating 550 F., unless some supplementary refluxing medium isused in the latter tower.

While the invention has been described particularly as applied to therecovery of uncondensed but condensable constituents from gas-vapormixtures from cracking operations, the invention is also useful in moregeneral applications for the recovery of such uncondensed butcondensable constituents from hydrocarbon gas mixtures from othersources, for example, from other refinery gases, tank gases and thelike.

We claim:

1. In cracking hydrocarbon oils, the improvement which comprises heatinga charge of oil to a cracking temperature under pressuretaking offvapors and gases therefrom and subjecting them to a condensingoperation, subjecting uncondensed vapors and gases from the condensingoperation to scrubbing treatment with raw oil to be supplied to thecracking operation, discharging residual oil from the first mentionedcharge of oil and reducing the pressure thereon, thereby causingvaporization of part of said residual oil, subjecting the resultingvapors to a refluxing operation, introducing raw oil with absorbedconstituents from the scrubbing treatment into direct contact with thevapors in this refluxing operation, and taking off and condensing thevapors from this refluxing operation.

2. In crackin provement whicfi hydrocarbon oils, the imcomprises heatinga charge of oil to a cracking temperature underpressure, dischargingresidual oil from this charge of oil and'reducing pressure thereon,

thereby causing vaporization of arts of said residual oil, subjectingthe resu ting vapors to a refluxing operation, subjecting a hydro-tcarbon gas mixture containing uncondensed but condensable hydrocarbonsto scrubbing treatment with raw oil to be supplied to the crackingoperation, introducin raw oil with absorbed constituents from t isscrubbingtreatment into direct contact with the vapors in the saidrefluxing operation, and taking off and condensing the vapors from thesaid refluxing operation.

3. In cracking hydrocarbon oils, the improvement which comprisessubjecting a hydrocarbon gas mixture containing uncondensed butcondensable constituents to scrubbing treatment with raw oil to besupplied to the cracking operation, discharging residual oil from thecracking operation, vaporizing absorbed constituents from the raw oilfrom the scrubbing operation while under a lower pressure than thatmaintained on the oil in the cracking operation by heat given up by thisdischarged residual oil, condensing the resulting vapors, and su plyingthe raw oil after vaporization of a sorbed constituents therefrom to thecracking operation.

In witness whereof, we have subscribed our names,

EUGENE O. HERTHEL. THOMAS DE COLON TIFFT.

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